Psychosis is a disorder which grossly interferes with the capacity to meet ordinary demands of life. Conceptually, it is a loss of ego boundaries or a gross impairment in reality testing. Included under the term pyschosis are the disorders Schizophrenia, Schizophreniform Disorder, Schizoaffective Disorder, Delusional Disorder, Brief Psychotic Disorder, Shared Psychotic Disorder, Psychotic Disorder due to a General Medical Condition, Substance-Induced Psychotic Disorder and Psychotic Disorder Not Otherwise Specified, as defined by the DIAGNOSTIC AND STATISTICAL MANUAL OF MENTAL DISORDERS, FOURTH EDITION, published 1994 by the American Psychiatric Association, Washington D.C. USA, incorporated herein by reference.
Schizophrenia is a disorder of thought which is characterized by positive (delusions, hallucinations, markedly bizarre behavior) and negative (flat affect, poverty of speech, social isolation, anhendonia) symptoms. The development of schizophrenia is thought to be due to an excess of dopaminergic transmission in the brain. This theory has been proposed based on the observations that typical antipsychotic drugs block D.sub.2 -type dopamine receptors, and drugs which increase the level of dopamine cause a psychosis that resembles the paranoid subtype of schizophrenia. Losoncyzy, M. F., et al., "The Dopamine Hypothesis of Schizophrenia", H. Y. Meltzer, ed., Psychopharmacology: The Third Generation of Progress. New York: Raven Press; 1987: 715-726.
There are presently therapeutic treatments available for treating psychosis by administering to the patient neuroleptic drugs such as chlorpromazine, haloperidol, and sulpride, for example. Of course, many of these drugs have unwanted side effects (e.g. extrapyramidal symptoms) or are not as effective as desired by all patients. Therefore, the need for different drug therapies still exists.